Staining of human teeth is caused mainly by calculus or plaque, or by adhesion of various staining substances on surfaces. Various physical or chemical methods have been presented as means of eliminating the cause of staining tooth surfaces. In addition to removal by polishing, physical methods include a method for removing staining substances by use of n-butyl ether, butyl butyrate, or the like (Patent Document 1, Patent Document 2), and a method for improving a color tone by covering a tooth by use of a ceramic veneer, etc. Known chemical methods include a method for promoting remineralization by an oral composition containing hydroxyapatite (Patent Document 3, Patent Document 4), a method for bleaching oxidatively by use of a peroxide (Patent Document 5), a method using a tooth whitening composition containing a peroxide as well as a self-curing calcium phosphate compound and a fluorine compound or the like (Patent Document 6), a method for promoting enamel remineralization by use of an oral composition containing a liquefied calcium phosphate compound (Patent Document 7), etc. Further, an oral composition using a combination of a polyvalent metal cation and polyphosphoric acid to prevent calculus and staining (Patent Document 8) is also known.
However, in case of the method using a ceramic veneer, etc., reduction of tooth mass is required, and for the use of the method a guidance or treatment by a dentist is required. Further, the method for bleaching oxidatively by use of a peroxide needs to use a high concentration of peroxide to allow teeth to be bleached oxidatively, and therefore it must be carried out cautiously under a guidance of a specialist. According to this method, although teeth can be whitened, the gloss is deteriorated. Furthermore, even under a guidance of a specialist, there are risks that the peroxide may damage teeth or gingiva, and cause hypersensitivity.
Meanwhile, the method for promoting remineralization of teeth by use of a calcium phosphate compound such as hydroxyapatite is mainly to repair enamel surfaces with apatite to thereby restore the tooth health, and is not satisfactory in terms of whitening effect. Further, in case of the combined use of polyphosphoric acid and a polyvalent metal cation, the whitening effect is not adequate again. None of such conventional whitening dentifrices can impart gloss to teeth, especially gloss to teeth themselves.
It has been known that phytic acid has activities, such as removal of tobacco tar, suppressive effect against calculus, and stabilization of stannous fluoride, and a cleansing agent and a dentifrice, each containing phytic acid have been reported (Patent Document 9), Further, to improve astringency in intraoral application of a composition containing phytic acid, known are various techniques of mixing phytic acid with an amphoteric electrolyte, such as an amino acid and a protein (Patent Document 10), a specific flavor component (Patent Document 11), a chain hydrocarbon compound (Patent Document 12), polyvinyl alcohol or polyvinylpyrrolidone (Patent Document 13), or the like. Further, to improve the astringency of a polyphosphate, a technique of mixing an alkali metal sulfate therewith is known (Patent Document 14).